Maternal control of mouse preimplantation development

The identification and classification of candidate genes during the zygotic genome activation in the mammals

Zygotic genome activation (ZGA) is a critical event in early embryonic development, and thousands of genes are involved in this delicate and sophisticated biological process. To date, however, only a handful of these genes have revealed their core functions in this special process, and therefore the roles of other genes still remain unclear. In the present study, we used previously published transcriptome profiling to identify potential key genes (candidate genes) in minor ZGA and major ZGA in both human and mouse specimens, and further identified the conserved genes across species. Our results showed that 887 and 760 genes, respectively, were thought to be specific to human and mouse in major ZGA, and the other 135 genes were considered to be orthologous genes. Moreover, the conserved genes were most enriched in rRNA processing in the nucleus and cytosol, ribonucleoprotein complex biogenesis, ribonucleoprotein complex assembly and ribosome large subunit biogenesis. The findings of this first comprehensive identification and characterization of candidate genes in minor and major ZGA provide relevant insights for future studies on ZGA.

Impaired Blastocyst Formation in Lnx2-Knockdown Mouse Embryos

Ligand of Numb-protein X 2 (LNX2) is an E3 ubiquitin ligase that is known to regulate Notch signaling by participating in NUMB protein degradation. Notch signaling is important for differentiation and proliferation in mammals, and plays a significant role in blastocyst formation during early embryonic development. In this study, we investigated Lnx2 in mouse preimplantation embryos. Expression analysis showed that Lnx2 is expressed in oocytes and preimplantation embryos. Lnx2-knockdown embryos normally progress to the morula stage, but the majority of them do not develop into normal blastocysts. Transcript analysis revealed that the expression levels of genes critical for cell lineage specification, including octamer-binding transcription factor 4 (Oct4), are increased in Lnx2 knockdown embryos. Furthermore, the expression levels of Notch and Hippo signaling-related genes are also increased by Lnx2 knockdown. Collectively, our results show that Lnx2 is important for blastocyst formation in mice, suggest that this may act via lineage specification of inner cell mass, and further show that Lnx2 may be involved in transcriptionally regulating various genes implicated in early embryonic development.

Comparative maternal protein profiling of mouse biparental and uniparental embryos

Background

Maternal proteins have important roles during early embryonic development. However, our understanding of maternal proteins is still very limited. The integrated analysis of mouse uniparental (parthenogenetic) and biparental (fertilized) embryos at the protein level creates a protein expression landscape that can be used to explore preimplantation mouse development.

Results

Using label-free quantitative mass spectrometry (MS) analysis, we report on the maternal proteome of mouse parthenogenetic embryos at pronucleus, 2-cell, 4-cell, 8-cell, morula, and blastocyst stages and highlight dynamic changes in protein expression. In addition, comparison of proteomic profiles of parthenogenotes and fertilized embryos highlights the different fates of maternal proteins. Enrichment analysis uncovered a set of maternal proteins that are strongly correlated with the subcortical maternal complex, and we report that in parthenogenotes, some of these maternal proteins escape the fate of protein degradation. Moreover, we identified a new maternal factor-Fbxw24, and highlight its importance in early embryonic development. We report that Fbxw24 interacts with Ddb1-Cul4b and may regulate maternal protein degradation in mouse.

Conclusions

Our study provides an invaluable resource for mechanistic analysis of maternal proteins and highlights the role of the novel maternal factor Fbw24 in regulating maternal protein degradation during preimplantation embryo development.

Contextualizing Autophagy during Gametogenesis and Preimplantation Embryonic Development

Mammals face environmental stressors throughout their lifespan, which may jeopardize cellular homeostasis. Hence, these organisms have acquired mechanisms to cope with stressors by sensing, repairing the damage, and reallocating resources to increase the odds of long-term survival. Autophagy is a pro-survival lysosome-mediated cytoplasm degradation pathway for organelle and macromolecule recycling. Furthermore, autophagy efflux increases, and this pathway becomes idiosyncratic depending upon developmental and environmental contexts. Mammalian germ cells and preimplantation embryos are attractive models for dissecting autophagy due to their metastable phenotypes during differentiation and exposure to varying environmental cues. The aim of this review is to explore autophagy during mammalian gametogenesis, fertilization and preimplantation embryonic development by contemplating its physiological role during development, under key stressors, and within the scope of assisted reproduction technologies.

The pivotal roles of the NOD-like receptors with a PYD domain, NLRPs, in oocytes and early embryo development†

Nucleotide-binding oligomerization domain (NOD)-like receptors with a pyrin domain (PYD), NLRPs, are pattern recognition receptors, well recognized for their important roles in innate immunity and apoptosis. However, several NLRPs have received attention for their new, specialized roles as maternally contributed genes important in reproduction and embryo development. Several NLRPs have been shown to be specifically expressed in oocytes and preimplantation embryos. Interestingly, and in line with divergent functions, NLRP genes reveal a complex evolutionary divergence. The most pronounced difference is the human-specific NLRP7 gene, not identified in rodents. However, mouse models have been extensively used to study maternally contributed NLRPs. The NLRP2 and NLRP5 proteins are components of the subcortical maternal complex (SCMC), which was recently identified as essential for mouse preimplantation development. The SCMC integrates multiple proteins, including KHDC3L, NLRP5, TLE6, OOEP, NLRP2, and PADI6. The NLRP5 (also known as MATER) has been extensively studied. In humans, inactivating variants in specific NLRP genes in the mother are associated with distinct phenotypes in the offspring, such as biparental hydatidiform moles (BiHMs) and preterm birth. Maternal-effect recessive mutations in KHDC3L and NLRP5 (and NLRP7) are associated with reduced reproductive outcomes, BiHM, and broad multilocus imprinting perturbations. The precise mechanisms of NLRPs are unknown, but research strongly indicates their pivotal roles in the establishment of genomic imprints and post-zygotic methylation maintenance, among other processes. Challenges for the future include translations of findings from the mouse model into human contexts and implementation in therapies and clinical fertility management.

DPAGT1-Mediated Protein N-Glycosylation Is Indispensable for Oocyte and Follicle Development in Mice

Post-translational modification of proteins by N-linked glycosylation is crucial for many life processes. However, the exact contribution of N-glycosylation to mammalian female reproduction remains largely undefined. Here, DPAGT1, the enzyme that catalyzes the first step of protein N-glycosylation, is identified to be indispensable for oocyte development in mice. Dpagt1 missense mutation (c. 497A>G; p. Asp166Gly) causes female subfertility without grossly affecting other functions. Mutant females ovulate fewer eggs owing to defective development of growing follicles. Mutant oocytes have a thin and fragile zona pellucida (ZP) due to the reduction in glycosylation of ZP proteins, and display poor developmental competence after fertilization in vitro. Moreover, completion of the first meiosis is accelerated in mutant oocytes, which is coincident with the elevation of aneuploidy. Mechanistically, transcriptomic analysis reveals the downregulation of a number of transcripts essential for oocyte meiotic progression and preimplantation development (e.g., Pttgt1, Esco2, Orc6, and Npm2) in mutant oocytes, which could account for the defects observed. Furthermore, conditional knockout of Dpagt1 in oocytes recapitulates the phenotypes observed in Dpagt1 mutant females, and causes complete infertility. Taken together, these data indicate that protein N-glycosylation in oocytes is essential for female fertility in mammals by specific control of oocyte development.

Ratio of the zygote cytoplasm to the paternal genome affects the reprogramming and developmental efficiency of androgenetic embryos

Uniparental embryos have uniparental genomes and are very useful models for studying the specific gene expression of parents or for exploring the biological significance of genomic imprinting in mammals. However, the early developmental efficiency of androgenetic embryos is significantly lower than that of parthenogenetic embryos. In addition, oocytes are able to reprogram sperm nuclei after fertilization to guarantee embryonic development by maternally derived reprogramming factors, which accumulate during oogenesis. However, the importance of maternal material in the efficiency of reprogramming the pronucleus of androgenetic embryos is not known. In this study, androgenetic embryos were constructed artificially by pronucleus transfer (PT) or double sperm injection (DS). Compared with DS embryos, PT embryos that were derived from two zygotes contained more maternal material, like 10-11 translocation methylcytosine deoxygenase 3 (Tet3) and histone variant 3.3 (H3.3). Our experiments confirmed the better developmental potential of PT embryos, which had higher blastocyst rates, a stronger expression of pluripotent genes, a lower expression of apoptotic genes, and superior blastocyst quality. Our findings indicate that the aggregation of more maternal materials in the paternal pronucleus facilitate the reprogramming of the paternal genome, improving embryonic development in PT androgenesis.

The Unique Mechanisms of Cellular Proliferation, Migration and Apoptosis are Regulated through Oocyte Maturational Development-A Complete Transcriptomic and Histochemical Study

The growth and development of oocyte affect the functional activities of the surrounding somatic cells. These cells are regulated by various types of hormones, proteins, metabolites, and regulatory molecules through gap communication, ultimately leading to the development and maturation of oocytes. The close association between somatic cells and oocytes, which together form the cumulus-oocyte complexes (COCs), and their bi-directional communication are crucial for the acquisition of developmental competences by the oocyte. In this study, oocytes were extracted from the ovaries obtained from crossbred landrace gilts and subjected to in vitro maturation. RNA isolated from those oocytes was used for the subsequent microarray analysis. The data obtained shows, for the first time, variable levels of gene expression (fold changes higher than |2| and adjusted p-value < 0.05) belonging to four ontological groups: regulation of cell proliferation (GO:0042127), regulation of cell migration (GO:0030334), and regulation of programmed cell death (GO:0043067) that can be used together as proliferation, migration or apoptosis markers. We have identified several genes of porcine oocytes (ID2, VEGFA, BTG2, ESR1, CCND2, EDNRA, ANGPTL4, TGFBR3, GJA1, LAMA2, KIT, TPM1, VCP, GRID2, MEF2C, RPS3A, PLD1, BTG3, CD47, MITF), whose expression after in vitro maturation (IVM) is downregulated with different degrees. Our results may be helpful in further elucidating the molecular basis and functional significance of a number of gene markers associated with the processes of migration, proliferation and angiogenesis occurring in COCs.

A role of Pumilio 1 in mammalian oocyte maturation and maternal phase of embryogenesis

Background

RNA binding proteins play a pivotal role during the oocyte-to-embryo transition and maternal phase of embryogenesis in invertebrates, but their function in these processes in mammalian systems remain largely understudied.

Results

Here we report that a member of the Pumilio/FBF family of RNA binding proteins in mice, Pumilio 1 (Pum1), is a maternal effect gene. The absence of maternal PUM1 in the oocyte does not affect meiotic maturation but leads to abnormal preimplantation development. Furthermore, genome-wide transcriptome analysis of oocytes and embryos revealed that there is a concomitant perturbation of the mRNA milieu. Of note, putative PUM1 mRNA targets were equally perturbed as non-direct targets, which indicates that PUM1 regulates the stability of maternal mRNAs both directly and indirectly. We show Cdk1 mRNA, a known PUM1 target essential for meiosis and preimplantation development, is not degraded appropriately during meiosis, leading to an increase in CDK1 protein in mature oocytes, which indicates that PUM1 post-transcriptionally regulates Cdk1 mRNA; this could partially explain the observed abnormal preimplantation development. Furthermore, our results show that maternal and zygotic PUM1 are required for postnatal survival.

Conclusions

These findings indicate that PUM1 is essential in the process of cytoplasmic maturation and developmental competence of the oocyte. These results reveal an important function of maternal PUM1 as a post-transcriptional regulator during mammalian embryogenesis.

Electronic supplementary material

The online version of this article (10.1186/s13578-018-0251-1) contains supplementary material, which is available to authorized users.

Functional signaling and gene regulatory networks between the oocyte and the surrounding cumulus cells

Background

The maturation and successful acquisition of developmental competence by an oocyte, the female gamete, during folliculogenesis is highly dependent on molecular interactions with somatic cells. Most of the cellular interactions identified, thus far, are modulated by growth factors, ions or metabolites. We hypothesized that this interaction is also modulated at the transcriptional level, which leads to the formation of gene regulatory networks between the oocyte and cumulus cells. We tested this hypothesis by analyzing transcriptome data from single oocytes and the surrounding cumulus cells collected from antral follicles employing an analytical framework to determine interdependencies at the transcript level.

Results

We overlapped our transcriptome data with putative protein-protein interactions and identified hundreds of ligand-receptor pairs that can transduce paracrine signaling between an oocyte and cumulus cells. We determined that 499 ligand-encoding genes expressed in oocytes and cumulus cells are functionally associated with transcription regulation (FDR < 0.05). Ligand-encoding genes with specific expression in oocytes or cumulus cells were enriched for biological functions that are likely associated with the coordinated formation of transzonal projections from cumulus cells that reach the oocyte’s membrane. Thousands of gene pairs exhibit significant linear co-expression (absolute correlation > 0.85, FDR < 1.8 × 10^− 5) patterns between oocytes and cumulus cells. Hundreds of co-expressing genes showed clustering patterns associated with biological functions (FDR < 0.5) necessary for a coordinated function between the oocyte and cumulus cells during folliculogenesis (i.e. regulation of transcription, translation, apoptosis, cell differentiation and transport).

Conclusion

Our analyses revealed a complex and functional gene regulatory circuit between the oocyte and surrounding cumulus cells. The regulatory profile of each cumulus-oocyte complex is likely associated with the oocytes’ developmental potential to derive an embryo.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4738-2) contains supplementary material, which is available to authorized users.

The Genetic Regulation of Cell Fate During Preimplantation Mouse Development

The adult body is estimated to contain several hundred distinct cell types, each with a specialized physiological function. Failure to maintain cell fate can lead to devastating diseases and cancer, but understanding how cell fates are assigned and maintained during animal development provides new opportunities for human health intervention. The mouse is a premier model for evaluating the genetic regulation of cell fate during development because of the wide variety of tools for measuring and manipulating gene expression levels, the ability to access embryos at desired developmental stages, and the similarities between mouse and human development, particularly during the early stages of development. During the first 3 days of mouse development, the preimplantation embryo sets aside cells that will contribute to the extraembryonic tissues. The extraembryonic tissues are essential for establishing pregnancy and ensuring normal fetal development in both mice and humans. Genetic analyses of mouse preimplantation development have permitted identification of genes that are essential for specification of the extraembryonic lineages. In this chapter, we review the tools and concepts of mouse preimplantation development. We describe genes that are essential for cell fate specification during preimplantation stages, and we describe diverse models proposed to account for the mechanisms of cell fate specification during early development.

Developmental block and programmed cell death in Bos indicus embryos: effects of protein supplementation source and developmental kinetics

The aims of this study were to determine if the protein source of the medium influences zebu embryo development and if developmental kinetics, developmental block and programmed cell death are related. The culture medium was supplemented with either fetal calf serum or bovine serum albumin. The embryos were classified as Fast (n = 1,235) or Slow (n = 485) based on the time required to reach the fourth cell cycle (48 h and 90 h post insemination - hpi -, respectively). The Slow group was further separated into two groups: those presenting exactly 4 cells at 48 hpi (Slow/4 cells) and those that reached the fourth cell cycle at 90 hpi (Slow). Blastocyst quality, DNA fragmentation, mitochondrial membrane potential and signs of apoptosis or necrosis were evaluated. The Slow group had higher incidence of developmental block than the Fast group. The embryos supplemented with fetal calf serum had lower quality. DNA fragmentation and mitochondrial membrane potential were absent in embryos at 48 hpi but present at 90 hpi. Early signs of apoptosis were more frequent in the Slow and Slow/4 cell groups than in the Fast group. We concluded that fetal calf serum reduces blastocyst development and quality, but the mechanism appears to be independent of DNA fragmentation. The apoptotic cells detected at 48 hpi reveal a possible mechanism of programmed cell death activation prior to genome activation. The apoptotic cells observed in the slow-developing embryos suggested a relationship between programmed cell death and embryonic developmental kinetics in zebu in vitro-produced embryos.

The use of mouse models to study epigenetics

Much of what we know about the role of epigenetics in the determination of phenotype has come from studies of inbred mice. Some unusual expression patterns arising from endogenous and transgenic murine alleles, such as the Agouti coat color alleles, have allowed the study of variegation, variable expressivity, transgenerational epigenetic inheritance, parent-of-origin effects, and position effects. These phenomena have taught us much about gene silencing and the probabilistic nature of epigenetic processes. Based on some of these alleles, large-scale mutagenesis screens have broadened our knowledge of epigenetic control by identifying and characterizing novel genes involved in these processes.